linux-kernel - Re: dm: free io_barrier after blk_cleanup

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Message-ID: <CAAeU0aMcaaMehJ31ANVFrwrC7YiCLW1dPosNujFtNyG9nOcC+g@mail.gmail.com>
Date:   Mon, 10 Oct 2016 07:52:05 -0700
From:   Tahsin Erdogan <tahsin@...gle.com>
To:     Mike Snitzer <snitzer@...hat.com>
Cc:     Alasdair Kergon <agk@...hat.com>, dm-devel@...hat.com,
        Shaohua Li <shli@...nel.org>, linux-raid@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: dm: free io_barrier after blk_cleanup_queue call

On Mon, Oct 10, 2016 at 6:25 AM, Mike Snitzer <snitzer@...hat.com> wrote:
> I have to believe this was born out of code inspection rather than
> actual need (due to crash, etc)?

This got originated from several crashes I have seen with 4.3 kernel.
The crashes
were caused by null dereferencing of io_barrier->per_cpu_ref.

The issue may no longer be relevant after commit c91852ff0815
("dm: optimize dm_request_fn()") because conditions for accessing
io_barrier may not longer exist. But fix should be considered for
forked stable trees.